Injection molding machines

ABSTRACT

There is provided a method and apparatus for molding laminar articles. Two screw-injection barrels sequentially pass resinous materials through a valve in a single sprue into a mold cavity. The valve is controlled so that material from one screw-injection barrel does not pass while material flows from the other screwinjection barrel. The control means is synchronized so that the desired quantities of materials from the two injection barrels are placed in the mold cavity.

Johnson Gamer inventor Welwyn Garden City, England App]. No. 781,763Filed Dec. 6, 1968 Patented Aug. 17, 1971 Assignee Imperial ChemicalIndustries Limited London, England Priority Dec. 15, 1967 Great Britain57081/67 INJECTION MOLDING MACHINES ll Claims,3 DrawingFigs.

18/30AA, 18/30 WJ, 264/328, 264/D1G. 57 Int. CL .Q A43d 3/00, B28b 1/24Field otSearch 18/30 AA,

30 NM, 30 NP, 30 NV, 30 NW, 30 NS, 30 NZ, 30 AS, 30 0?, 30 RV, 30 W], 30UC, 30 UM, 30 US, 94-96, DIG. 59; 164/337; 264/245, 328

2,656,568 10/1953 Watkins 18/30 3,466,700 9/1969 Harrison...... 18/302,279,380 4/1942 Reid 18/30 3,192,581 7/1965 Sylvester 164/95 X3,221,373 12/1965 Lun Fat Kwan 264/245 FOREIGN PATENTS 865,403 4/1961Great Britain 18/30 RV 1,234,978 2/1967 Germany 18/30 VK 1,007,0534/1957 Germany.... 18/30 AA 1,195,860 5/1959 France. 18/30 AA PrimaryExaminerRichard .1, Herbs! Assistant Examiner-R. M. RogersAuorney-Cushman, Darby & Cushman ABSTRACT: There is provided a methodand apparatus for molding laminar articles. Two screw-injection barrelssequentially pass resinous materials through a valve in a single sprueinto a mold cavity. The valve is controlled so that material from onescrew-injection barrel does not pass while material flows from the otherscrew-injection barrel. The control (med means is synchronized so thatthe desired quantities of materi- UNITED STATES PATENTS als from the twoinjection barrels are placed in the mold cavi- 2,174,779 10/1939 Decorme264/245 ty.

PATENTEUAUBWQYI W8 290 sum 2 or 3 INJECTION MOLDING MACHINES The presentinvention relates to improvements in or relating to injection-moldingmachines;

lt has been proposed to produce laminar articles by the sequentialinjection of two materials into a mold. If, however, it is necessary toproduce an injection-molding article having a core of a certain materialand surface layers of a different material, mixing of the two materialsmay be reduced if they are injected sequentially from one port into themold. In this way the material forming the surface layers of the articleis the first to be injected in the mold and is then forced to theextremities of the mold by the pressure due to the injection of thecore-forming material thus ensuring'that the surface layer material doesin fact provide the whole of the surface. To ensure that there is asharp distinction between the two materials it is desirable that theyshould be prevented from mixing before they are injected into the mold.

According to the present invention we provide in an injection-moldingmachine for thermoplastic materials in which material is introduced tothe mold from at least twoseparate sources along a single sprue a valveadapted to permit only material from one of said sources to'enter saidsprue at any one instance of time and that only allows the total amountof material required from that sprue in the production of one molding topass therethrough during one molding cycle.

Throughout the present specification and claims the term sprue" is usedto describe the channel connecting the valve to the mold cavity.

The present invention is particularly, but not exclusively, applicableto the production of articles having a foamed core and unfoamed surfacelayers. These articles may be produced by first injecting an unfoamablethermoplastic composition into the mold and subsequently injecting afoamable composition, which is then allowed to foam in the mold. Theunfoamable composition thus provides the unfoamed surface skin of thearticle. Conveniently these articles may be made in an injection moldingmachine having two injection barrels both of which introducethermoplastic material into a single sprue from whence the material isinjected into the mold. Thus, using an injection-molding machineaccording to the present invention the valve is first opened to thesource of unfoamable material and the desired amount of unfoamablematerial introduced into the sprue and mold cavity; the valve is thenclosed to the unfoamable material and opened to the source of foamablematerial and the required amount of foamable material allowed to passthrough the valve and into the mold. The foamable material is thenallowed to foam within the mold; this foaming may be permitted byinjecting only an amount of material into the mold so that the mold willbe filled when foaming has taken place. Alternatively the mold cavitymay be enlarged subsequent to the injection to provide room for thefoamable material to expand. The mold may be enlarged mechanically or bythe pressure generated by the decomposition of the blowing agent as isconvenient. The valve should be closed to all the sources of materialafter the required amounts of material have been injected into the sprueand the mold to prevent further material from dribbling from the sourcesinto the sprue and to prevent material being forced back through thevalve due to the pressures generated by the foaming of the foamablematerial within the mold.

ln a preferred method of operating a machine according to the presentinvention which is especially useful in the production of laminararticles having a foamed core with unfoamed surface skins a secondcharge of unfoamable composition is allowed to pass through the valveafter the charge of the foamable composition. This second charge ofunfoamable material may be derived from a third source of material or,as is preferred, it may come from the same source as the original chargeof unfoamable material. The first of these alternatives involves the useof a three-way valve whereas the second technique involves a secondswitching of the two-way valve.

The purpose of introducing a second charge of unfoamable material istwofold. Firstly,'although most of the material in the sprue is removedwith the molding, there is generally some left in the sprue and thesecond charge of unfoamable material ensures that any material thatremains in the sprue when the molding is removed from the mold isunfoamable material.

This desirable because if there is some foamable material remaining inthe sprue this will become part of the first charge of material used inthe next molding cycle and the presence of blowing agent in this firstcharge will tend to mar the surface finish of the article produced. Thesecond purpose is that it ensures that, when the material that was inthe sprue during molding and is attached to the molding when it isremoved from the mold is cut away from the molding, an unfoamed and nota foamed area is exposed.

The valve provided by the present invention may conveniently comprise atap provided with a bore corresponding to each source of material, eabhbore being adapted to permit material to flow from one of the source ofmaterial into the sprue, the bores being so disposed in the tap thatwhile material may flow from one source i into the sprue, material isprevented from flowing from the other sources. Then, by switching thetap, material is permitted to flow from another source while beingprevented from flowing from any of the others, the preferred form ofvalve may also be shut off from all the sources of material to preventmaterial from dribbling through the valve due to thermal expansion ofmaterial in the sources. Furthermore, once the valve has been shut offafter the introduction of the materials the screw of the molding machinemay be retracted ready for the next molding cycle and it is notnecessary to wait until molding has been completed. This therefore meansthat the process may be operated more quickly. The bores of the tap mayconveniently be brought into and out of register with the sources ofmaterial and into the shutoff position either by rotation orreciprocation of the tap. Our preferred molding machines contain twosources of material which are preferably barrels of injectionmoldingmachines and the channels from these sources should preferably enter thevalve separately and emerge from the valve along a single channelledsprue. If the channels join after they have emerged from the valve thereis a risk that the materials in the two channels will be mixed. Thevalve may conveniently be formed in the barrel end cap of a moldingmachine or may be formed in the fixed platen of the machine or in ablock attached to the fixed platen or in the mold itself. ln ourpreferred machine the valve is formed in the barrel end cap of a moldingmachine consisting of two injection barrels which are preferablyparallel to each other.

The present invention is applicable to the injection molding of anythermoplastic materials. The materials from the separate sources may bethe same thermoplastic or different as the case may be. Although the useof machines according to this invention has been described withparticular reference to the injection molding of articles having afoamed core and smooth surface layers, the invention is in no waylimited to the production of such articles. For example, it may be usedto produce articles comprising laminates of two different thermoplasticmaterials or two different colors of the same or different thermoplasticmaterials.

The molding machines of the present invention may be of the type inwhich material is introduced to the mold through more than one sprue andin the operation of such machines the material from one or more of thesesprues may be provided by the technique of the present invention. lnthis instance the total amount of material that is allowed to flowthrough the valve during one molding cycle should be the amount that isrequired from that source in the final molding and will not then be thequantity required to fill the mold. If, on the other hand, the onlysupply of material to the mold is along a sprue which is fed by morethan one source of material according to the present invention, then theamount that is allowed to pass through the valve in one molding cyclewill be the amount required to produce the molding. Whichever techniqueis used, we prefer that the valve is switched to allow no more materialto pass therethrough once the required quantity has been introduced to,the mold and sprue.

The timing of the operation of the machine according to the presentinvention must be synchronized so that the various operations involvedtake place at the correct time. Thus, firstly the mold is closed readyfor the introduction of the molding material; the valve is then openedto the first source of material and the required quantity injectedthrough the valve into the sprue; the valve then switched and materialfrom the next source injected and so on for each source. The valve maythen be closed or switched again to a final source or back to the firstsource as is required. The valve is then closed, the pressure on thematerial in the mold from one of the sources, being maintained until thevalve is closed. Finally, if necessary the mold is enlarged to allow anyfoaming to take place and the mold then opened and the molding removed.The cycle may then be repeated.

The present invention is illustrated but in no way limited by referenceto the accompanying drawings in which: R

FIG. I is a section through the part of an injection-molding machinecontaining a valve according to the present invention; and

FIG. 2 is a section taken on AA' of FIG. 1, and

FIG. 3 is a section through the mold and barrels of another form ofmachine according to the present invention.

With'reference to FIG. 1 the injection machine comprises two injectionbarrels I and 2 both of which deliver material into the sprue 3 andthence into the mold 4. The valve 5 is positioned in the paths of flowof the materials flowing from the two barrels; the valve is providedwith two bores 6 and 7, the bore 6 being adapted to allowimaterial toflow from barrel 1 through the valve into the sprue and the bore 7 beingadapted to allow material to flow from barrel 2 through the valve intothe sprue.

In operation of the machine illustrated in FIG. I the valve is set toallow material to flow from one of the barrels, barrel 1 as shown inFIG. I, into the sprue and when the desired amount of material hasflowed from barrel 1 the valve is rotated as shown by the arrow so thatbore 6 is taken out of register with barrel 1 and bore 7 is brought intoregister with barrel 2. Materials may then flow from barrel 2 into thesprue and the whole charge, including the original material from barrel1, injected into the mold.

FIG. 2 is a cross section along A'-A of FIG. 1 and illustrates how thebores 6 and 7 are formed in the tap.

In the machine illustrated in FIG. 3 material is delivered to the moldfrom the barrels of two injection units 8 and 9 into the mold 10 alongthe sprue 11 to form the molding illustrated by the area 12. The mold 10is located between the platens of the mold l3 and 14. The material flowsfrom injection barrel 9 along channel 15 and from barrel 8 along channel16. These two channels converge in the barrel end cap of the machine andmeet at the selector valve 17; the valve 17 is provided with two boreseach of which may be brought into register with one of the channels 15and 16 to allow material to flow therefrom into the sprue 11 whilepreventing material from flowing from the other channel. The valve maybe switched from one source to the other and into a shutoff position byrotation of the valve rod 18.

lclaim:

I. An injection-molding machine for molding laminar articles having anouter surface layer and at least one inner core layer of resinousmaterial wherein at least two of the layers are composed of differentresinous compositions, comprising a first screw-injection barreloperably connected through a sprue to a mold cavity for injecting afirst resinous material through the sprue and into the mold cavity, atleast one additional screw-injection barrel operably connected throughsaid sprue to said mold cavity for injecting at least one additionalresinous material which is different in composition from said firstresinous material through said sprue and into said mold ca vit a valvemeans for passing the resinous material from said irst and additionalscrew-in ection barrels to said mold,

said valve means being operably connected to the said screwinjectionbarrels and said sprue, control means for the valve means forcontrolling, in sequence, the passing of resinous material from saidfirst screw-injection barrel into the sprue, then the passing ofresinous material from said additional screw-injection barrel into thesprue and then for preventing resinous material from passing from any ofsaid screw barrels into said sprue and for preventing any resinousmaterial from passing back out of said mold into the sprue, and meansfor synchronizing the control means for said valve means during amolding cycle, whereby a predetermined quantity of said first resinousmaterial is injected into the mold and whereby a predetermined quantityof said additional resinous material is thereafter injected into themold.

2. An injection-molding machine according to claim 1 in which the valvecomprises a tap provided with channels, each of which is adapted topermit material to flow from one of the barrels into the sprue and byswitching the tap material is then permitted to flow from another ofsaid barrels into the sprue and which may be switched to prevent anymaterial flowing into the sprue.

3. An injection-molding machine according to claim 2 in which the valveis formed in the barrel end cap of the molding machine.

4. A injection-molding machine according to claim 1 in which there areonly two separate screw-injection barrels.

5. An injection-molding machine according to claim 1 in which thebarrels of two injection-molding machines are aligned parallel to eachother.

6. A process for the production of resinous laminates having an outersurface layer and at least one inner core layer comprising:

l. injecting a first resin from a first injection barrel through a sprueand into a mold cavity;

2. injecting an additional resin of a different composition from anadditional injection barrel through the same said sprue, into the samesaid mold cavity and into the said first resin;

. operating a valve in communication with the said first and saidadditional injection barrels and in communication with and positionedbetween said sprue and said first and said additional injection barrels;

4. controlling the operation of the valve to allow resin to pass, insequence, first from said first injection barrel into said mold cavityand then to allow said additional resin to pass from said additionalinjection barrel into said mold cavity and into said first resin andsaid controlling of the valve being such to prevent resin passing backout of said mold cavity; and

5. timing the operation of the valve whereby predetermined quantities ofthe first and additional resins are injected into the mold cavity.

7. A process according to claim 6 in which at least one resin is athermoplastic material.

8. A process according to claim 6 in which the resin which is injectedfrom said additional barrel is a foamable resin.

9. A process according to claim 8 in which after the resins have beeninjected into the mold, the mold cavity is enlarged to allow thefoamable resin to foam.

10. A process according to claim 8 in which a second charge ofunfoamable resin is introduced into the sprue after the charge offoamable resin.

11. A process according to claim 10 in which the second charge ofunfoamable resin is derived from the first injection barrel and isobtained by switching the valve back to the first barrel after therequired amount of foamable resin has been introduced into the moldcavity, to allow further unfoamable resin to be introduced into the moldcavity.

2. An injection-molding machine according to claim 1 in which the valvecomprises a tap provided with channels, each of which is adapted topermit material to flow from one of the barrels into the sprue and byswitching the tap material is then permitted to flow from another ofsaid barrels into the sprue and which may be switched to prevent anymaterial flowing into the sprue.
 2. injecting an additional resin of aDifferent composition from an additional injection barrel through thesame said sprue, into the same said mold cavity and into the said firstresin;
 3. An injection-molding machine according to claim 2 in which thevalve is formed in the barrel end cap of the molding machine. 3.operating a valve in communication with the said first and saidadditional injection barrels and in communication with and positionedbetween said sprue and said first and said additional injection barrels;4. controlling the operation of the valve to allow resin to pass, insequence, first from said first injection barrel into said mold cavityand then to allow said additional resin to pass from said additionalinjection barrel into said mold cavity and into said first resin andsaid controlling of the valve being such to prevent resin passing backout of said mold cavity; and
 4. A injection-molding machine according toclaim 1 in which there are only two separate screw-injection barrels. 5.An injection-molding machine according to claim 1 in which the barrelsof two injection-molding machines are aligned parallel to each other. 5.timing the operation of the valve whereby predetermined quantities ofthe first and additional resins are injected into the mold cavity.
 6. Aprocess for the production of resinous laminates having an outer surfacelayer and at least one inner core layer comprising:
 7. A processaccording to claim 6 in which at least one resin is a thermoplasticmaterial.
 8. A process according to claim 6 in which the resin which isinjected from said additional barrel is a foamable resin.
 9. A processaccording to claim 8 in which after the resins have been injected intothe mold, the mold cavity is enlarged to allow the foamable resin tofoam.
 10. A process according to claim 8 in which a second charge ofunfoamable resin is introduced into the sprue after the charge offoamable resin.
 11. A process according to claim 10 in which the secondcharge of unfoamable resin is derived from the first injection barreland is obtained by switching the valve back to the first barrel afterthe required amount of foamable resin has been introduced into the moldcavity, to allow further unfoamable resin to be introduced into the moldcavity.